1. Field of the Invention
The present invention relates to a method and an apparatus for breaking-in a wet clutch.
2. Description of the Related Art
A known wet clutch is used, for example, as a lockup clutch incorporated in a torque converter. A torque converter with a lockup clutch normally has problems, in which unpleasant vibration, so-called judder, is likely to occur due to stick slip. Since this vibration is produced by large changes of the friction coefficient in the friction-contact surfaces of clutch, the vibration can be significantly reduced or eliminated by leveling the friction coefficient through breaking-in of the wet clutch beforehand.
Japanese patent application laid-open No. Hei 6-26530 describes a break-in method for a multiplate friction engagement device, that is, another type of wet clutch, in which the surface of a clutch plate of the engagement device is finished to a predetermined surface roughness (0.1-0.4 .mu.Ra) by rotating the clutch plate in the friction contact with an abrasive in an oil.
However, since this break-in method merely breaks in the clutch plate, that is, the counter member of a friction member (clutch disc), the friction coefficient of the friction contact surfaces will change when the engagement device is incorporated into a transmission. Thus, this method has problems in that the finishing of the clutch plate to a predetermined roughness does not readily reduce the vibration.
Instead of using the abrasive, the friction member can be used to break in the clutch plate together with the friction member (also described in the aforementioned patent application). However, since the friction contact conditions change when the friction member and the clutch plate are assembled into a transmission, the break-in achieved by this method is not sufficiently maintained in the final product. Thus this method still finds it difficult to significantly reduce the vibration.